The present invention relates to a surface treatment composition for glass fibers, a method of coating glass fibers with said composition, and a method of preparing glass fiber reinforced polyepoxide products.
A number of fiber reinforced plastics are used commercially for various purposes. Articles such as sheets, tapes or fabrics wherein fibers are impregnated with resins such as polyimide, bismaleimide-triazine or preferably an epoxy are referred to as prepreg substrates. One important use of prepreg substrates is to provide a surface upon which a pattern of an electrical conductor can be provided to obtain circuit boards or circuit cards. The printed circuit boards or cards in turn are prepared from laminates of multiple layers of glass fiber impregnated epoxy resin compositions.
Among many factors governing the characteristics of a glass fiber/epoxy composite the fiber/matrix interface is considered to be the most sensitive region in the composite Weak adhesion in this region leads to defects such as delamination, blistering, plate back and the like, which seriously impede function, reliability and manufacturing yield of printed circuit boards. Therefore, increased board size, reduced circuitry dimensions, and increased operating temperatures of advanced multilayer boards require improved glass fiber/epoxy adhesion to achieve the required high quality standards.
To enhance the adhesion between these two-phase materials and to preserve it against moisture attack, it is a common practice to use coupling agents for improving the bond strength of epoxy or other resins to glass fiber surfaces. The most commonly used coupling agents are organosilane compounds of the general formula X.sub.3 Si(CH.sub.2).sub.n Y, in which n is an integer from 0 to 3, X is a hydrolyzable group and Y is an organofunctional group which is compatible and/or reactive with a given polymer matrix. Particularly useful silanes are gamma-aminopropyltriethoxysilane or 3-glycidoxypropyltrimethoxysilane.
U.S. Pat. No. 3,702,783 teaches the improvement in glass-resin bonding achieved by the employment of a mixture of 3-glycidoxypropyltrimethoxysilane as organofunctional silane and a methyltrialkoxysilane.
U.S. Pat. No. 4,500,600 teaches aqueous size compositions for glass fibers comprising gamma-aminopropyltriethoxysilane and alkoxysilanes.
U.S. Pat. No. 3,576,031 teaches organosilanes having at least one chemically-combined aliphatically unsaturated imido-organic radical (e.g., maleimidosubstituted organo-silane) and a method for making these materials. Said compounds can be employed to impart improved surface characteristics to cellulosic substrates and to make aliphatically unsaturated imido-substituted organopolysiloxanes
In order to improve laminate performance even under extremely adverse environments, one major concern is to provide tenacious adhesion between the fibrous substrate and the resin composition. Although the use of silanes and especially amino- and glycidoxy-substituted silanes as mentioned above has proved to provide quite good adhesion with resin compositions, there still remains room for additional enhancement in the bonding strength between the resin, particularly epoxy resin, and the glass fiber substrate.
Therefore, an object of the invention is a new class of organosilane compounds with significantly improved adhesion characteristics that promises to provide significantly improved properties for advanced composite applications.